1. Field of the Invention
The present invention relates to a hydraulic booster to be used in a closed and/or open hydraulic circuit, and more particularly, to a hydraulic booster for actuating a braking system or a clutch releasing device or a motor vehicle.
2. Description of the Prior Art
A hydraulic booster including a control valve mechanism of a spool valve type has disadvantages with respect to required accuracy of finishing of the control valve mechanism, an amount of leakage of pressurized hydraulic fluid from the control valve mechanism, and inoperability of the control valve mechanism caused by foreign material in the hydraulic fluid as compared with a hydraulic booster including a control valve mechanism of a poppet valve type.
In the conventional hydraulic booster including the control valve mechanism of poppet valve type, however, the valve member for controlling hydraulic communication between a working chamber and a drain chamber which are positioned at opposite sides of a power piston is urged by the hydraulic pressure in the working chamber toward the drain chamber under an operating condition of the booster, thereby causing a relatively larger hysterisis of the operational character of the booster. In addition, the conventional control valve mechanism needs a relatively larger space for positioning thereof.
In addition, in a hydraulic booster provided with an open circuit, it is desirable to provide a damping means for preventing an input member from vibration caused by pulsation of a pump.